An integrated circuit (“IC”) die may be assembled into an IC package by physically and electrically coupling it to a substrate made of organic or ceramic material. One or more IC packages may be physically and electrically coupled to a printed circuit board (“PCB”) to form an “electronic assembly”. The “electronic assembly” may be part of an “electronic system”. An “electronic system” is broadly defined herein as any product comprising an “electronic assembly”. Examples of electronic systems include computers (e.g., server, router, desktop, laptop, hand-held, Web appliance, etc.), wireless communications devices (e.g., cellular phone, cordless phone, pager, computer with wireless network, etc.), computer-related peripherals (e.g., printer, scanner, monitor, wireless network card, etc.), entertainment devices (e.g., television, radio, stereo, tape and compact disc players, video cassette recorder, camcorder, digital camera, MP3 (Motion Picture Experts Group, Audio Layer 3) player, etc.), and the like.
An IC die may comprise one or more active and/or passive circuits. At least one surface of the die may comprise a number of pads or contacts to couple the die functionally to another element, such as an IC substrate. Two or more die may be stacked in a single package.
An IC substrate may comprise a number of layers. Some layers may comprise organic or ceramic dielectric material. Some layers may comprise conductors, such as traces, ground planes, and vias. An IC substrate may include an electronic component mounted on a surface of the substrate. The electronic component may be functionally connected to other elements of an electronic system through a hierarchy of conductors that include substrate traces, ground planes, and vias. The conductors may carry signals that are transmitted among the electronic components, such as IC's, of the system. An IC substrate may have a relatively large number of input/output (“I/O”) terminals (also called “lands”), as well as a large number of power and ground terminals or lands, on a surface of the IC substrate.
In the field of electronics, it is known to apply a material, commonly referred to as “underfill”, around and over the electrical connections between various components. One purpose of underfill is to increase adhesion between components that are electrically connected (e.g. via solder). Underfill is also used to absorb mechanical shock forces between internal components when an electronic system, such as a cellular telephone or hand-held computer, is inadvertently dropped. Without underfill, the electrical connections between components may be broken or disconnected. Another purpose of underfill is to provide a sealed environment to inhibit the intrusion of water or other contaminants. In addition, underfill may be used to decrease potentially harmful flexing forces on a component, such as a die mounted on a package substrate.
It is known to apply underfill subsequent to mounting an electronic component on a packaging element. For example, purchasers of IC's may apply underfill after they mount IC's on PCB's in the process of manufacturing electronic systems. Such purchasers buy the underfill and apply it as part of manufacturing operations. Such underfill may take the form of an epoxy that is applied after reflow and that may be cured in a subsequent heating operation after reflow.